A procedure performed to evaluate the presence of blockages and plaque buildup in the carotid arteries in the neck that supply blood flow to the brain. Plaque buildup in this artery can lead to a stroke. Usually an ultrasound exam result will suggest a blockage that will lead to this test. If a severe blockage is found, it can be fixed by surgery, or in some cases, by inserting a stent into the artery to hold open the artery and cage off any plaque that may be at risk of causing strokes.